Decolorization of aqueous glyoxal solutions

Abstract

An aqueous glyoxal solution is decolorized by a process in which the said solution is passed over granulated active carbon which is arranged in a fixed bed and whose differential pore radius distribution has a maximum of from 10 to 100 A, the Peclet number being from 500 to 5000, the decolorized glyoxal solution is discharged, the active carbon bed is then regenerated by treating it with an aqueous solution of an alkaline agent and then with an aqueous acid, and further glyoxal solution to be decolorized is passed over the active carbon regenerated in this manner.

We claim: 
     
       1. A process for decolorizing an aqueous glyoxal solution which process comprises: passing said solution over a granulated active carbon which is arranged in a fixed bed and which has a maximum differential pore radius distribution of from 10 to 100 A, the Peclet number being from 500 to 5000,   discharging the decolorized glyoxal solution from said bed,   then regenerating the active carbon bed at a temperature up to 90° C. by first treating it with an aqueous solution of an alkaline agent and then with an aqueous acid, and   again passing further glyoxal solution to be decolorized over the active carbon bed regenerated in this manner.   
     
     
       2. A process as claimed in claim 1, wherein a 10-60% strength by weight aqueous glyoxal solution is decolorized. 
     
     
       3. A process as claimed in claim 1, wherein a 0.2-10% strength by weight sodium hydroxide solution or potassium hydroxide solution is used as the aqueous solution of an alkaline agent for the regeneration. 
     
     
       4. A process as claimed in claim 1, wherein a 0.5-15% strength by weight nitric acid is used as the aqueous acid for the regeneration. 
     
     
       5. A process as claimed in claim 1, wherein, the regeneration steps are carried out at about room temperature. 
     
     
       6. A process as claimed in claim 1, wherein the granulated active carbon has a particle size of from 0.5 to 2.5 mm. 
     
     
       7. A process as claimed in claim 1, wherein the granulated active carbon has a maximum differential pore radius distribution of 20 to 50 A and a Peclet number of from 1500 to 3000. 
     
     
       8. A process as claimed in claim 7, wherein the granulated active carbon has a particle size of from 0.9 to 1.3 mm. 
     
     
       9. A process as claimed in claim 8, wherein the regeneration steps are carried out at about room temperature. 
     
     
       10. A process as claimed in claim 7, wherein the regeneration steps are carried out at about room temperature. 
     
     
       11. A process as claimed in claim 1, wherein a 10-60% strength glyoxal solution is continuously decolorized to a color number equal to or less than 10 APHA, and the granulated active carbon is regenerated before the color number exceeds this value of 10 APHA. 
     
     
       12. A process as claimed in claim 11, wherein the regeneration steps are carried out at about room temperature. 
     
     
       13. A process as claimed in claim 12, wherein the granulated active carbon has a particle size of from 0.5 to 2.5 mm., a maximum differential pore radius of 20 to 50 A and a Peclet number of from 1500 to 3000. 
     
     
       14. A process as claimed in claim 13, wherein the aqueous solution of an alkylating agent is a 0.2-10% strength by weight sodium or potassium hydroxide solution, and the aqueous acid is a 0.5-15% by weight nitric acid.